Multifrequency-based sharpening of focal volume

Systems that emit electromagnetic or sonic waves for diagnostic or interventional applications are often limited by the size of their aperture, thus producing an elongated beam. Here, we have developed a method that substantially sharpens the depth of focus. The method superimposes a range of frequencies in space and time, and does not require labeling of targets or other manipulations of the medium. Using simulations, we found that the method sharpens the depth of focus even for systems with a narrow bandwidth. Moreover, we implemented the method in ultrasonic hardware and found that a ±23% frequency bandwidth provides an average 7.4-fold reduction in the focal volume of the resulting beams. This method can be readily applied to sharpen the focus of interventional systems and is expected to also improve the axial resolution of existing imaging systems.